The end grain of wood is more porous than face grain. Because of this, end grain absorbs more stain, typically resulting in a darker surface than that of the face grain. There are two techniques for controlling end grain absorption: One is to seal the end grain so it absorbs less color, and the other is to sand the end grain smoother than the face grain.
Either works well with all wood species.
I find that the most effective approach is to combine the two techniques. I first apply
Controlling Color 154
To prevent heavy stain absorption on the end grain of this panel, the author seals it with a dilute coat of shellac, then sands it with 400-grit paper before staining. The panel was sealed before assembly to avoid getting the sealer on other parts.
The right side of this oak board was washcoated with 1-lb.-cut shellac before being stained with an oil-based stain.
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Controlling Color 155 Splotching is a common staining problem
with some woods. To prevent it on this cherry board, the bottom half of the board was washcoated with glue size prior to being stained with an alcohol dye.
Selecting a Washcoat
When choosing a washcoat, select one that won’t be dissolved by the stain solvents.
Here’s a guide to basic compatibility.
GLUE SIZE SHELLAC LACQUER-BASED1 WATER-BASED2
Oil-based stain x x x
Lacquer/fast-dry stain x Water-based stain
(pre-mixed) x
Water-soluble dyes x x x
Alcohol-soluble dyes x
NGR stain x
1. Sanding sealer or vinyl sealer, thinned 2:1 thinner/finish 2. Water-based thinned 2:1 water/finish or premixed stain controller
The splotchy hemlock spindle at left was not sealed before staining. The two others were first washcoated with glue size. The spindle at far right was stained twice with the same color of stain to get the dark color desired.
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There are a handful of techniques for preventing splotching. You can use a gel stain or a water-based dye stain, both of which will minimize or eliminate splotch-ing. You can preseal the surface to regulate stain absorption, or spray the stain to ensure a more consistent absorption. Another choice is to apply the color in the form of a toner, as discussed in Section 8. Of course you could also prevent the problem by avoiding stain altogether—simply applying a clear finish to your project. If you like, you can use a strongly colored finish as a “stain.”
Any one of the above methods will work on even the most splotch-prone woods, as I’ll discuss below. You can also combine the techniques for the greatest flexibility in achieving the color you want.
Using Gel Stains
Because of their thick consistency, gel stains are remarkably good at not penetrating too deeply. They work well on most softwoods but can exhibit a lack of clarity. However, applying a gel stain over a washcoat, as dis-cussed next, almost guarantees a splotch-free stained surface.
Preloading and Applying a Washcoat The most effective form of splotch control involves sealing the wood with a clear, highly thinned finish before applying the stain. While the principle behind this tech-nique is simple, it can seem confusing because of the number of different prod-ucts used. When shopping for the various sealers, you’ll encounter premixed products with names like Pre-Stain, Stain
Controller, Wood Conditioner, Wood Stabilizer and even Glue Size. In addition, Understand that the culprit here is not
the stain. The fault lies in the way the wood’s structure reacts to the stain.
Although there are quite a few techniques for preventing splotching, there isn’t any sin-gle solution that works with all woods.
That’s why it’s important to be able to iden-tify woods that will splotch and to practice the various solutions on scrap before staining your workpiece.
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To check for poten-tial splotching problems before applying stain, wipe the wood with a non-grain-raising solvent like naph-tha, mineral spirits, alcohol, or lacquer thinner. The figured cherry at left will splotch, but not the cherry plywood at right.
One approach to avoiding splotching is to avoid staining altogether. Instead you can simply use a strongly colored finish like the two shellacs or varnish
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I use preloading stain controllers for oil-based wiping stains. As a general rule, they are a good choice when you have a lot of area to stain or you simply wish to avoid the sanding involved after applying a washcoat, as described next.
Washcoat stain controllers are thinned fin-ishes that are applied to the wood surface and then allowed to dry before being sanded.
(Some oil-based commercial washcoats do not require sanding.) They all work by plug-you can make plug-your own sealers by mixing
various finishes with thinner.
But don’t be confused. All these products basically serve the same purpose—to control the amount of stain that soaks into the wood. Their differences lie mainly in the type of resin and solvents they use and how they are applied. For the sake of clarity, I’ll divide them into two basic classes: “preload-ing stain controllers” and “washcoat stain controllers.” Each of these is distinguished by its method of application, which should be described on the containers of the various premixed products.
Preloading stain controllers are applied by flooding the surface with an oil-based prod-uct, then allowing it to sit for 10 to 15 min-utes before applying the stain on top of the still-wet controller. You can use a premixed controller or make your own by mixing 1 part boiled linseed or tung oil with 9 parts mineral spirits. These products are typically sold for use with oil-based wiping stains.
Controlling Color 157 Glue size is available in a concentrated
liq-uid that is to be diluted with water. It makes fuzzy woods easier to sand, and it seals end grain to prevent excessive stain absorption.